Apparatus and methods for safely providing hazardous reactants

ABSTRACT

An apparatus for providing a reactant comprises a reactant space and a reservoir space. The reactant space comprises a chemical complex capable of evolving the reactant when heated. The reservoir space, in turn, is in gas communication with the reactant space. The apparatus is operative to heat the chemical complex when a pressure of the reactant in the reservoir space is below a predetermined set-point, and to cool the chemical complex when the pressure of the reactant in the reservoir space is above the predetermined set-point.

FIELD OF THE INVENTION

This invention relates to chemical sources, and, more particularly, toapparatus and methods for providing hazardous reactants such ashydrazine while mitigating hazards associated with storage,environmental spills, and over-production.

BACKGROUND OF THE INVENTION

Hazardous reactive chemicals are commonly used as reactants to promotechemical vapor deposition (CVD), atomic layer deposition (ALD), andother processes. Some of these chemicals are particularly unstable anddangerous. For example, CVD and ALD growth of a variety of nitride filmshave been demonstrated with the aid of hydrazine (N₂H₄) as the nitrogenand reducing source with superior process performance and filmproperties over other, less reactive nitrogen sources. Nevertheless, theuse of hydrazine in commercial CVD and ALD processes has been hamperedby concerns about the safety implications of this extremely unstable,explosive, and hazardous chemical reactant.

Generally speaking, hydrazine is a low cost chemical widely used in thechemical industry for a variety of processes. Hydrazine and hydrazinederivatives are also being used as rocket propellants. Overall annualproduction of hydrazine typically exceeds 50,000 tons. With theexception of propellants, hydrazine is typically stored, transported,and used in the much safer aqueous solutions ranging from 35-64weight-percent (wt %). For applications such as CVD and ALD, however,these aqueous solutions are typically disadvantageous. In particular,most applications require high-purity anhydrous hydrazine with itsassociated safety and toxicity issues. A spill of liquid anhydroushydrazine may easily self ignite, raise the localized temperature and,as a result, the localized partial pressure, and ultimately detonatewhen the localized partial pressure in air exceeds 4.7% and thelocalized temperature exceeds 92 degrees Celsius (° C.). The explosiondamage coupled with the spread of toxic NO and NO₂ by-products can becatastrophic. The potential danger from anhydrous hydrazine spills makesit unpopular as a rocket propellant, let alone as an industrial chemicalreactant. Accordingly, hydrazine derivatives such as monomethylhydrazineand dimethylhydrazine have been invoked as safer substitutions.Unfortunately, both derivatives have found very limited use in processessuch as CVD and ALD due to their lower reactivity and the tendency toinclude carbon in films.

Hydrazine cyanurate (HC) is a stable complex of hydrazine that wasdeveloped and made public by Nachbaur and Leiseder for the purpose ofpurification and separation as early as 1971. When heated above 170° C.,HC decomposes into the ingredients hydrazine and cyanuric acid (CA).Hydrazine production from HC depends on the temperature and the quantityof HC. In the temperature range between 170-245° C., the partialpressure of CA is negligible. Above 245° C., CA disadvantageouslydecomposes into hydrocyanic acid. Otherwise, when HC is relatively cold(i.e. below about 100° C.), it is stable and safe. These characteristicsled others to propose HC for industrial hydrazine production purposes.More particularly, T. J. Kropewnicki et al. in “Hydrazine Cyanurate as aNitrogen Source for Thin Nitride Film Growth,” Journal of Vacuum Scienceand Technology A16(1), January/February 1998, pp. 139-144; and K. J.Taylor et al. in U.S. Pat. No. 6,465,350, entitled “Aluminum NitrideFilm Formation on Integrated Circuits,” propose forming hydrazine fromHC for CVD nitridization reactions. Nevertheless, these references onlyset forth methodologies consisting of heating HC to an elevatedtemperature (e.g., 210° C.) and simply leaving it at this temperaturewhile one or several CVD reaction sequences are allowed to run. Noregard is paid to the consistency of the hydrazine supply within a givenCVD sequence or from one sequence to the next, to the potential for thecatastrophic accumulation of hydrazine in the reactor or the heatedsource due to overproduction and condensation, or to compensating forthe drop in hydrazine production as hydrazine in the HC source isexhausted. As a result, even with these various attempts to harnesshydrazine from HC, HC has seen no significant implementation inindustrial deposition processes despite the many well known benefits ofusing hydrazine as a reactant and despite the availability of HC forover 35 years.

Low-volatility chemicals can be consistently maintained at a desiredpartial pressure when placed in an elevated temperature container. Thisstable vapor pressure at a given temperature ensures the consistency ofchemical supply and an automatic, per-demand, supplementation of thesource to maintain the desired pressure. For example, during processing,the source chemical is being drawn into the process chamber toeffectively drive the partial pressure down and subsequently drive morechemical into the gas phase to maintain the equilibrium vapor pressure.

Evolving hydrazine from HC is fundamentally different. Hydrazineevolution from HC is a continuous process that produces substantialquantities of hydrazine for as long as the source temperature issufficiently high. For example, about 1.8×10⁻⁸ grams/sec of hydrazine isproduced per each gram of HC at 170° C., as detailed below. FIG. 1displays hydrazine production versus time, normalized to one gram of HC,as measured from the pressure rise inside a ˜2 liter (L) container.Clearly, the rate of hydrazine production increases at highertemperatures. The absolute rates of hydrazine production are estimatedfrom the given known volume and the potency of HC. These rates were usedto extract the kinetics of hydrazine production, as displayed in FIG. 2.A good fit to a linear dependence of log(rate) versus 1/T, wherein T isthe absolute temperature, indicates a first order Arrhenius behaviorwith an activation energy of 48±2 kilocalories per mole and thenormalized rate is given by: k (hydrazine production/gram ofHC)=6±2×10¹⁵ exp(−(24,000±1,000)/T) grams/sec. Accordingly, significantproduction of hydrazine does not start at temperatures lower than about170° C. At room temperature (i.e., 25° C.), for example, hydrazineproduction is negligibly low at 4×10⁻²³ grams/sec/gram-of-HC. At thatrate, one kilogram (kg) of HC will require almost 800 years to produce anegligible one nanogram of hydrazine. However, at 200° C., one kgproduces 550 micrograms in one second. At 230° C., which is recommendedas the highest safe temperature for HC heating (with ˜15° C. margin),hydrazine production from one kg of HC reaches ˜40 grams/hour.

Production of hydrazine at any given temperature is clearly a continuousprocess that declines with the exhaustion of the HC load. Sincehydrazine is being continuously produced, it clearly lacks any mechanismto ensure that this hazardous chemical is not over-produced andconsequently accumulates beyond demand. Eventually, over-production ofhydrazine may exceed the dew point at the given source temperature andexcess hydrazine may condense into liquid anhydrous hydrazine. Forexample, if the temperature of a 1 kg HC load is maintained at 200° C.,the initial production rate of ˜0.0330 grams/min will exceed thedew-point pressure of 55 Torr after approximately 15 minutes within a 5L source chamber maintained at 50° C. At that point the source willstart accumulating hazardous liquid anhydrous hydrazine. Indeed, theinventors observed that hydrazine production did not produce anypressure rise above ˜18 Torr when the source chamber temperature wasmaintained at 32° C., suggesting condensation. Upon heating the sourcechamber to 40° C., the pressure instantaneously rose to ˜28 Torr andthen saturated there. Although production rate will slow down with theexhaustion of HC, it will produce ten grams of liquid anhydroushydrazine within approximately five hours. This over-production ofhydrazine may defeat the purpose of using HC as a means for on-demandproduction of hydrazine. Likewise, there is no mechanism to ensureadequate supplementation of hydrazine to compensate for process usage.Hydrazine production at any given temperature scales with the potency ofHC which inevitably declines as the HC adduct (i.e., chemical complex)breaks down into hydrazine and CA. Therefore, if the HC temperature isminimized to minimize over production during idle time, it may soon betoo low for consistent hydrazine supply during processing, especiallysince the potency of HC will decline during usage as explained below.

To further demonstrate the major drawbacks of prior art practice whereinHC is maintained at a constant temperature, the inventors monitored thepressure of hydrazine inside a 2 L source chamber during a TiN ALDprocess using a “Synchronous Modulation of Flow and Draw” ALD process inaccordance with aspects of U.S. Pat. No. 6,911,092, entitled “ALDApparatus and Method,” to one of the presently named inventors, which ishereby incorporated by reference herein. Hydrazine was produced from HCat a controlled temperature of 185° C. The TiN process appliedsaturating TiCl₄ and hydrazine pulses to grow a high quality film at a270° C. process temperature. Likewise, a 50 milliseconds (msec) pulse ofhydrazine from a source pressure of 8 Torr generated a dose of ˜50μgrams of hydrazine, which was sufficient to saturate the hydrazinereaction. FIG. 3 (solid line) displays the pressure of hydrazine withinthe source chamber during a first idle time, a first process wherein thehydrazine was pulsed for 50 msec, a second idle time, a second processwherein the hydrazine was pulsed for 100 msec, a third idle time, and athird process wherein the hydrazine was pulsed for 200 msec. In eachprocess, the TiCl₄ was pulsed for 30 msec, which was sufficient toachieve saturation. FIG. 3 demonstrates that the practice of the priorart is neither safe nor suitable for consistent delivery of hydrazine.Hydrazine production was continuous during idle-times. During theprocess periods, the production of hydrazine clearly lagged behind theutilization as indicated by the dramatic pressure drops. In fact, thedose/cycle varied between 105 and 5 μgrams/pulse, 385 and 33μgrams/pulse, and 736 and 7 μgrams/pulse over the first, second andthird process runs, respectively, making any attempt to use the priorart practice for processing hopeless. There was also evidence fordeclining production rates with the usage of HC. For example, theaverage production rate declined from 1.0275×10⁻⁷ grams/sec/gram-of-HCduring the first idle time to 1.0230×10⁻⁷ and 1.0216×10⁻⁷ during thesecond and third idle times, respectively. That was a 0.4% and 0.6% ratedecrease for relatively short processes running consecutively.

In summary, a hydrazine supply, when simply held at a constanttemperature, may vary by a great factor given the dependence on multipleparameters such as HC potency, initial load, temperature, the extent ofprevious idle time where hydrazine was produced but not consumed, andthe extent of previous processing wherein hydrazine may have beenconsumed faster than produced. These variations could easily span anorder of magnitude as shown in the example of FIG. 3. At that level ofsource inconsistency, even state of the art chemical deliveryinstruments such as mass flow controllers (MFC) or pressure controllers(PRC) might be driven into instability. Given the lack of consistency,and the lack of dependable mechanisms to prevent over production and toreact to process related withdrawal or idle-time related consumptionhalts, the simple constant-temperature HC source of the prior art isneither safe nor suitable for process applications such as CVD and ALD.

Therefore, there is a need for apparatus and methods that can harnessrelatively stable, easily-handled chemical complexes of hazardousreactants such as HC into safe and consistent on-demand chemical sourcesfor processes such as CVD, ALD, surface preparation, surface and bulktreatment, and reactive abatement.

SUMMARY OF THE INVENTION

Embodiments of the present invention address the above-identified needsby providing apparatus and methods for safely providing hazardousreactants such as, but not limited to, hydrazine.

In accordance with an aspect of the invention, an apparatus forproviding a reactant comprises a reactant space and a reservoir space.The reactant space comprises a chemical complex capable of evolving thereactant when heated. The reservoir space, in turn, is in gascommunication with the reactant space. The apparatus is operative toheat the chemical complex when a pressure of the reactant in thereservoir space is below a predetermined set-point, and to cool thechemical complex when the pressure of the reactant in the reservoirspace is above the predetermined set-point.

In accordance with another aspect of the invention, a reactant isprovided at least in part by placing a chemical complex that is capableof evolving the reactant when heated into a reactant space. A reservoirspace is placed in gas communication with the reactant space.Subsequently, the chemical complex is heated when a pressure of thereactant in the reservoir space is below a predetermined set-point, andcooled when the pressure of the reactant in the reservoir space is abovethe predetermined set-point.

For example, one of the above-identified embodiments comprises anapparatus that enables safe and consistent on-demand production ofhydrazine from HC. The HC is housed in a cartridge that is in gascommunication with a reservoir chamber. The apparatus causes thecartridge to be heated when the hydrazine pressure in the reservoirchamber drops below a set-point value (e.g., 100 Torr) and causes thereservoir to be cooled when the hydrazine pressure in the reservoirchamber exceeds the set-point value. In this manner, hydrazineproduction is limited to achieving and maintaining the set-pointpressure. The reservoir, in turn, supplies the hydrazine to a sourcechamber through a pressure control valve. The pressure control valveacts to hold the hydrazine pressure at a predetermined pressure suitablefor use in processing with the hydrazine. Temperature zones in theapparatus maintain the apparatus above the dew-point temperature of thehydrazine to avoid condensation. In addition, several valves andinterlocks provide a means of safely handling the reactant if a fault isdetected. Once so formed, the hydrazine can be used for a plurality ofuses including nitride formation, oxide formation, surfacecleaning/termination, gas abatement, and surface modification.Downstream abatement elements neutralize any unconsumed hydrazine beforeit is vented into the atmosphere.

Advantageously, embodiments in accordance with aspects of the inventioncorrelate production with demand to maintain consistent and properdelivery of hydrazine during processing and terminate production duringidle times. Dangers associated with storage, environmental spills, andover-production are thereby mitigated.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a chart showing hydrazine production versus time at differenttemperatures normalized to one gram of HC;

FIG. 2 is a chart showing the kinetics of hydrazine production;

FIG. 3 shows a chart of hydrazine pressure during three consecutiveprocess/idle sequences under prior art conditions, as well as theperformance of an apparatus in accordance with an illustrativeembodiment of the invention;

FIG. 4 shows a flow schematic of an apparatus in accordance with anillustrative embodiment of the invention;

FIG. 5 shows a front perspective view of a portion of the FIG. 4apparatus;

FIG. 6 shows a chart of hydrazine condensation temperature as a functionof pressure; and

FIG. 7 shows an electrical schematic of an additive pressure and atemperature control circuit for use in the FIG. 4 apparatus.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described with reference to illustrativeembodiments. More particularly, the following embodiments surround theproduction of the reactant hydrazine from the chemical complex HC.Nevertheless, numerous modifications can be made to these embodimentsand the results will still come within the scope of the invention. Nolimitations with respect to the specific embodiments described hereinare intended or should be inferred.

FIG. 4 illustrates a flow schematic of an apparatus 100 in accordancewith an illustrative embodiment of the invention for film formation(e.g., film growth and film deposition). The apparatus comprisescartridge 110 used to store and transport HC, wherein a load of HCadduct is placed within cartridge chamber 111 (i.e., the “reactantspace”). Cartridge 110 also comprises manual shutoff valve 112, forexample, a high temperature diaphragm valve. The cartridge 110 isattached to source chamber assembly 120 comprising a reservoir 121(i.e., the “reservoir space”) equipped with pressure gauge 122 andnormally-open vent valve 123. A normally-closed control valve 125connects reservoir 121 to source chamber 127 (i.e., the “source space”).Valve 125 allows cartridge 110 removal without compromising theintegrity of the source chamber 127, as well as pressure control withinsource chamber 127. To execute pressure control, a pressure set-point iscompared to the reading of pressure gauge 129 and subsequently used tocontrol the position of control valve 125.

Control valve 125 is interlocked to de-energize in case there is anyfault in the system such as an over-temperature cartridge 110, anover-pressure delivery manifold, or indications of hydrazinecondensation (discussed below). Reservoir 121 serves as a pressurecontrolled reservoir wherein reservoir pressure, as measured by pressuregauge 122, is used to control hydrazine production rate. As taught inthis invention, hydrazine production from HC heating bears practicallimitations for cost effective modulation due to finite cartridgechamber 111 heating and cooling rates and the heat capacity of theloaded cartridge. Therefore, in the present embodiment, the combinationof hydrazine production to maintain pressure within reservoir 121 andthe pressure control in source chamber 127 provides consistent processpressure and accommodates the substantially abrupt on/off change inhydrazine demand between process/idle modes (i.e., processing modeswherein the apparatus 100 is actively forming films, and idle modeswherein the apparatus 100 is not actively forming films).

The temperature of the cartridge thermal zone 113 is controlled toachieve a required set reservoir pressure as measured by pressure gauge122. This set-point pressure is determined by the need of a specificprocess to ensure consistent hydrazine supply when the process switchesfrom idle to process. The cartridge chamber 111 is attached with goodthermal contact to heating/cooling block 114 (see also FIG. 5). Forexample, the block includes a heat exchanger flow path wherein air orcooling fluid is passed to reduce the temperature of the cartridgechamber 111 quickly. The heat exchanger can be used to raise thetemperature quickly by passing a hot fluid. Alternatively, heating maybe accomplished by other means of heating such as resistive heating,radiant heating, etc. The apparatus 100 is setup such that theheating/cooling block 114 is normally-cooling. If the pressure asmeasured by pressure gauge 122 is lower than the set-point, thenormally-cooling block 114 is temporarily switched into heating.“Normally cooling” means that the non-activated position is cooling. Inother words, it means that cooling is the default state if an interlockis triggered or any other fault such as loss of power and cabledisconnections occurs. Likewise, “normally-open valves” refer to valvesthat are open when not energized and “normally-closed valves” refer tovalves that are closed when not energized. Normally-open vent valve 123is typically energized to shut when hydrazine is produced. In the eventof apparatus failure or power loss, vent valve 123 will open and ventany excess hydrazine into vent manifold 150, which is properly equippedwith a vacuum pump, as well as a means to abate excess hydrazine safelyand monitor the exhaust of the pump for unabated hazards such ashydrazine or hydrazine abatement by-products such as NO and NO₂.

Clearly, the apparatus 100 can take several physical forms. FIG. 5 showsa perspective view of a portion of one such form. In this figure, thecartridge 110 (with its cartridge thermal zone 113) sits atop the sourcechamber 127. Resistive heater 114′ allows heating of the cartridge,while inlet and outlet ports 114″ and 114″, respectively, allow thecirculating of cooling fluid. The bottom of the thermal shield oftemperature zone 128 is also illustrated. Lastly, pressure gauge 129 andvalve 130 are shown.

Optionally, control valve 125 and pressure gauge 129 may be substitutedby a pressure controller such as the MKS 640A series, available from MKSInstruments (Andover, Mass., USA). In another variant meant forprocesses such as CVD, control valve 125 and pressure gauge 129 can alsobe substituted by a MFC. In such an alternative embodiment, the supplyof hydrazine to the process applies mass-flow rather than pressurecontrol. In any case, whether using MFCs or PRCs, care should be takento ensure that material of construction of the MFCs or PRCs arecompatible with hydrazine. Such devices may include, for example, theMKS 640A12TW1DA2D or the MKS1150C, but both require customization toreplace a nickel gasket with a stainless steel or Kalrez gasket.Pressure gauges that incorporate materials compatible with hydrazine aretypically suitable for the application. For example, MKS Model 728pressure gauges are heated to 100° C. for accurate and absolute pressuremeasurements. The Model 728 internal parts include only Inconel and 316series stainless steel, both compatible with hydrazine. Care should beused to use stainless steel gaskets instead of more commonly used nickelgaskets in common fittings such as VCR fittings. Hydrazine compatibilityinformation is available in, for example, NASA's Propellant/MaterialsCompatibility Program and Results (1982); AIAA Paper No. 75-1245 (1975);and Space Propulsion Lectures by Prof. Manuel Martinez-Sanchez—Lecture5: Hydrazine, p. 2-5.

The temperature of cartridge thermal zone 113 is also restricted by atleast two normally-closed temperature snap switches wired in series toensure that the temperature will never exceed a pre-set value.Temperature sensitive snap switches suitable for such an application arecommercially available from Tempco Electric Heater Corporation (WoodDale, Ill., USA), for example, the TEV05200 (NC) and TEV05201 (NO).Preferably, the pre-set maximum temperature of zone 113 is selected toensure that, given the temperature set-point of the snap switches,hysteresis, and a safety margin, the temperature will never exceed 245°C. This maximum temperature ensures the stability of CA and prevents theevolution of hydrocyanic acid. Preferably, the switches are wired torequire manual reset if snapped in order to resume power.

For even greater safety, manual valve 112 is preferably equipped withposition sensors. The heaters of cartridge thermal zone 113 areinterlocked to normally shut (with concurrent switching to the defaultcooling) if valve 112 is not in its fully open position. As the HCadduct (i.e., the chemical complex) draws to exhaustion, it requireshigher temperatures to maintain production. The cartridge 110 eventuallyreaches the maximum pre-set temperature wherein the temperature snapswitches trigger source shutoff. There are no solid condensablesubstances that could be produced and accumulate in the path betweencartridge chamber 111 and reservoir 121. However, if for some reason thepath between cartridge 110 and source chamber assembly 120 is blocked,the temperature of zone 113 will quickly rise in an attempt to reach theset pressure and will eventually reach over temperature and trigger thethermal snap switches to terminate hydrazine production at the source.In this case, the cartridge 110 evacuation may not be possible and thecartridge will contain a minute quantity of hydrazine. Manual valve 112will be shut to contain the cartridge chamber 111 and allow safetransfer into an isolated area such as a glove box wherein the cartridgecan be serviced.

As further indicated in FIG. 4, the source chamber 127 has an output toa delivery manifold 140 through a safety shutoff valve 130. Safetyshutoff valve 130 is preferably implemented using a properly selectednormally-closed ultrahigh purity (UHP) valve. Source chamber 127 may beset as a second heated zone 128, if needed, to prevent condensation.This zone includes the reservoir 121, pressure gauge 122, valve 123,pressure gauge 129, and both inlet and outlet valves 125 and 130,respectively. The temperature of zone 128 should be set significantlyhigher than the dew point of the set pressure to eliminate condensationas known in the art. To maintain failure safety, normally-opentemperature snap switches (closed when they go above pre-settemperature) are installed within temperature zone 128 to ensure thatthe temperature within that zone stays well above condensationtemperature. In the event the temperature of zone 128 falls below presettemperature, the interlock system will deactivate zone 113 heating andrevert to the normally-on cooling and the source pressure will be ventedinto downstream vent manifold 150.

Downstream from valve 130, delivery manifold 140 comprises pressuregauge 143 and normally-open relief valve 144. Manifold 140 connects thechemical source to the process apparatus 170 comprising process chamber173. This connection is facilitated though line 142 and inlet valve 171.The manifold 140 may be set as a third heated zone 141, if needed, againto prevent condensation. This zone includes relief valve 144 as well.Typically, inlet valve 171 is located within a separate temperature zone172 of the process chamber 173. Care should be taken to ensure that thetemperature of heated zone 172 is equal or higher than the temperatureof heated zone 141, or at the very least, higher than the dew point ofhydrazine at the delivery pressure. Relief valve 144 is used to venthydrazine out of the source chamber 127 and delivery manifold 144 if theapparatus 100 is disabled by the interlock system. Downstream from valve144, vent manifold 150 comprises normally-closed valve 153 connecting topump 154 and a suitably selected scrubber 155. Normally-closed valve 153de-energizes if the pressure, as measured by pressure gauge 151, exceedsa safety set-point to ensure that hydrazine vent does not occur if thevacuum pump 154 fails or the manifold 150 develops a large leak. Ventedhydrazine is scrubbed in scrubber 155 to ensure safe exhaust 157, asdetected by a properly selected exhaust monitoring sensor 156.

To further ensure safety in case of a failure, the production ofhydrazine is interlocked to the safe availability of the vent manifold150. That means that hydrazine production will be disabled if manifold150 is not fully functional. Accordingly, cartridge thermal zone 113 isnormally turned off and the cooling is turned on if the pressure inpumping line 152, as measured by pressure gauge 151, is higher than apreset set-point. Additionally, this interlock includes verification fornormal and satisfactory operation of pump 154 and scrubber 155, meaningthat they are operating below threshold-level-value (TLV) concentrationsof hazardous emissions as detected by exhaust monitoring sensor 156. Theinterlocks are preferably arranged in a fault safe manner, as know tothose skilled in the art. Vent manifold 150 is also utilized to evacuatereservoir 121 if over-pressure at gauge 122 is triggered or in the eventof any other fault. Accordingly, in such a situation, normally-open ventvalve 123 will open and excess hydrazine will be vented through line152.

Condensation of liquid hydrazine poses a substantial risk because it mayresult in the undetected overproduction of excess hydrazine within theapparatus 100. If the temperatures of source chamber assembly 120,delivery manifold 140, or process apparatus 170 are lower than thedew-point at the set-point pressure, undetected over-production ofhydrazine may occur. To prevent condensation, the temperatures of sourcecomponents downstream from cartridge 110 should be higher, preferablysignificantly higher, than the dew point of the hydrazine at thecontrolled pressure. FIG. 6 displays the dew point (condensation)temperature of hydrazine as a function of pressure. It is recommended tokeep the temperature of zones 128, 141, and 172 significantly higherthan the dew-point temperatures indicated in this chart.

For improved safety, the temperatures of zones 128, 141 and 172 are alsopreferably monitored by normally-open temperature snap switches andinterlocked to immediately stop hydrazine production if these switchessnap when the temperature in any zone drops below the pre-determinedsafety margin. Accordingly, preventing condensation within sourcechamber 127 and other components related to temperature zone 128 isstraightforward. In particular, components within zone 128 arepreferably integrated into the construction of source chamber 127.Thermally controlled chamber walls and components should be maintainedat temperatures that are at least 10° C. above the dew point of acontrolled hydrazine pressure. Temperature snap switches are typicallyaccurate within ±5° C. at the best and also suffer from a typical 10° C.hysteresis. Accordingly, zone 128 temperature should be set such thatthe lowest possible snap temperature of the normally-open snap switchesshould be a comfortable margin above the dew point.

To verify that condensation is not occurring, the source chamber 127 maybe set at the desired set pressure and then isolated by closing bothvalve 125 and valve 130. If there is no condensation, the pressureshould stay substantially steady as measured by pressure gauge 129. Incontrast, a steady pressure drop may indicate that condensation is notcompletely eliminated. These tests should be thoroughly conductedwhenever the pressure set-point (or the maximum pressure set-point) ischanged, as well as periodically, as part of the equipment processverification.

Likewise, a condensation test should be executed periodically on thereservoir 121 and the delivery manifold 140. The reservoir 121 can beisolated with valves 112 and 125, and monitored by pressure gauge 122.The delivery manifold can be isolated with valves 130, 171, and 144, andmonitored by pressure gauge 143.

Leaks should automatically halt production of hydrazine by artificiallyraising the pressure above set-point. It is also recommended toimplement a redundancy of pressure measurements such as more than onepressure gauge at reservoir 121 (i.e., doubling up on pressure gauge122). Alternatively, pressure gauge 143 may act as a backup pressuregauge for pressure gauge 129 when valve 130 is open.

Referring to the hydrazine production kinetics as presented in FIG. 2, aproper and safe hydrazine source may require cartridge temperaturemodulations of several tens of degrees between idle and process modes.For example, an exemplary TiN ALD process (discussed in greater detailbelow in the Section labeled “Exemplary Process No. 1”) was found torequire an initial temperature of 186° C. during processing (needed toproduce ˜1.2×10⁻⁴ grams/sec from a 1 kg load of HC), and an initialtemperature of 160° C. during idle (needed to slow the production ofhydrazine by a factor of >20). This 26° C. temperature change, in turn,requires ˜65 kilojoules (kJ) for a 1 kg HC cartridge with an estimatedheat capacity of 2,500 joules/degrees-Celsius (J/° C.) (for bothcartridge and HC load). Accordingly, a heating/cooling capacity of˜1,080 watts (W) allows the temperature change to occur in 1 minute.

While this heating/cooling capacity may be achieved by, for example,resistive heating and cooling with a fluid heat exchanger, the actualheating/cooling requirements in actual practice may be substantiallymore moderate. For example, 50 nanometers (nm) of TiN requires ˜0.06grams of hydrazine in a 1000 cycle process over an 8 minute period.However, a 0.25 L reservoir 121 set to a pressure of 100 Torr beforeprocessing starts already holds ˜0.047 grams of hydrazine. Moreover,consistent delivery of hydrazine at 8 Torr from the source chamber 127only requires that the reservoir 121 holds a pressure slightly abovethat (e.g., ˜10 Torr). Accordingly, if the reservoir is, in fact,pre-charged to about 100 Torr before processing, the ˜30° C. temperatureramp-up the reservoir 121 need only occur within ˜5 minutes in orderadequately catch up with the depletion of reservoir pressure. In thisway, the presence of the reservoir chamber 121 substantially reduces theneed for heating capacity. A 5 minute ramp-up of 30° C. requires only˜230 W heating power.

In addition, the end of the process and termination of hydrazine demanddrives a small rise of reservoir pressure which switches temperaturezone 113 from heating to cooling. Concurrently, valve 125 shuts the pathbetween reservoir 121 and source chamber 127. Even with a moderatecooling time of 10 minutes, source pressure remains close to set-point,as displayed in FIG. 3 (dashed line). At the same time, the accumulationof ˜0.02 grams of hydrazine, which is reasonably safe, elevates thepressure within the 0.25 L reservoir 121 by up to 20 Torr above thereservoir set-point. The accumulation of hydrazine in reservoir 121brings the available hydrazine within the reservoir up to ˜0.067 gramswhich exceeds the process usage by ˜24%. In the next cycle, the extra 20Torr pressure is initially used while the cartridge thermal zone 113stays in cooling mode. After ˜160 sec. the reservoir pressure dropsbelow 100 Ton and triggers the heating. This time catchup with hydrazinedraw starts at the 1 minute to-go mark (only 1 minute before thedeposition process ends) with the moderate heating time of ˜5 minutes.Clearly, a properly sized reservoir significantly decouples theproduction of hydrazine from the actual demand while at the same timepreserving: hydrazine production that is tied to demand, the existenceof only small quantities of anhydrous vapor at any given time, and theconsistent supply of hydrazine at steady pressure and/or steady flow.

Importantly, this configuration consistently accommodates hydrazinesupply during processing and a quick switching into idle mode with mildcooling and heating capacities (e.g., 100-250 W). The accumulation ofexcess hydrazine up to about 0.025 grams during a long idle time is notan intolerable tradeoff. For example, substantially long idle times,namely, idle 2 of 50 minutes and idle 3 of 25 minutes, were testedbetween successive TiN ALD process runs as displayed in FIG. 3. Thesequence of process 1, idle 2, process 2, idle 3, and process 3 withhydrazine usage of 1.2×10⁻⁴, 0, 2.4×10⁻⁴, 0, and 4.8×10⁻⁴ grams/sec,respectively was accommodated with a reservoir chamber 121 and sourcechamber 127 of 0.25 and 1.75 L, respectively, to yield a consistentsupply pressure of 8.01±0.06 Torr per set-point of 8.00 Torr asdisplayed in the figure (dotted line curve). Importantly, when a lot ofparts such as wafers are coated sequentially with more standard idletimes between wafers in the range of 2-5 minutes, reservoir 121moderates the temperature modulation needed to sustain the consistencyof the source chamber 127. This moderation is the result of a successiveprocesses starting sooner than an idle-time-period capable ofsubstantially reducing hydrazine production. For example, zone 113temperatures drops by only 5-7° C. during 2 minute idle times. Duringsuch short idle times, hydrazine accumulation of 0.012 grams withinreservoir chamber 121 (25.5 Torr pressure increase) is available tosustain the source pressure when the process again starts drawinghydrazine. The excess hydrazine lasts for ˜100 sec. and then triggersthe HC heating. The HC temperature is then elevated 5-7° C. during thenext minute.

Preferably, reservoir chamber 121 volume is selected such that it canaccommodate as many different processes as needed within thecontrollable pressure range. However, it is also recommended to keep theaccumulation within the reservoir at the minimum. For example,processing that typically implements short idle times, as in the case ofsequential runs of wafers, could preferably implement smaller overallpressure×volume as the typical temperature modulations are not expectedto be substantial.

Reducing the cartridge temperature below 120 is typically not necessaryas the rate of hydrazine production falls by the factorexp(24,000/T₁-24,000/T₂), which is 6500 times lower than the rate at186° C. For example, per the specific example detailed above, the ratedrops from ˜1.2×10⁻⁴ grams/sec at 186° C. down to 1.85×10⁻⁸ grams/sec(per 1 kg load of HC) at 120° C., meaning that accumulation of hydrazinewithin 24 hours is less than 0.0016 grams. That is equivalent to lessthan a 4 Torr pressure rise. Similarly, reservoir pressure rise duringan idle period of 1 hour at even 140° C. is less than a 3 Torr pressurerise. Accordingly, an embodiment may be switched from reservoir pressurecontrol into constant temperature control during long idle time. It can,for example, be set to 140° C. for idle times of several hours, and to120° C. for idle times of longer duration.

Two proportional-integral-derivative (PID) controllers are used tocontrol the heating/cooling of cartridge thermal zone 113. Suchcontrollers may, for example, comprise SD-series controllers from Watlow(St. Louis, Mo., USA). The control system 200 is illustrated in FIG. 7,wherein first PID controller 210 is configured for thermocouple 211input. The thermocouple is compensated by cold junction 212. Theamplified thermocouple reading is compared with set-point 213 bycomparator 214 and converted into a duty cycle dependenttransistor-transistor logic (TTL) signal by integrated circuit (IC) 215,as known in the art. Set-point 213 (e.g., 120° C.) is provided by theuser from the front panel of the first controller and sets the minimumtemperature to which the HC will be cooled. Alternatively, set-point 213is provided by remote through an appropriate controller such as aprogrammable logic controller (PLC), as also known in the art.

The second PID controller 220 is configured to compare the reservoirpressure 221 and the pressure set-point 222. Set-point 222 is determinedby the user from the front panel of the PID controller (e.g., 100 Torr).Alternatively, set-point 222 is provided by remote through anappropriate controller such as a PLC, as known in the art. Comparator223 is used to compare the pressure to the set-point. Next, IC 224converts the output of comparator 223 into a duty cycle of TTL.Subsequently, the duty cycle TTL from both IC 215 and IC 224 are addedby AND gate 230. Next, the combined TTL is split into cooling circuit250 and heating circuit 260. The TTL is inverted by NOT gate 251 andused to activate relay 252, which controls the cooling apparatus 253inverse to the heating. The non-inverted TTL is used to activate relay261 to connect the heating power phase 262 through the heater to theneutral 263 to drive resistive heater 271 and heat cartridge 270.

Accordingly, when pressure set-point 222 is equal or higher thanpressure 221 (i.e., during idle time), the duty cycle of IC 224 is zero.However, the temperature 211 is still substantially higher than thetemperature set-point (for the lowest possible temperature during idle)213. Therefore, the duty cycle of IC 215 is also zero. The duty cyclecoming out of AND gate 230 is zero. As a result, relay 261 never turnson—i.e. heating is off. In contrast, the inverted duty cycle is always 5VDC (“high”), therefore continuously driving relay 252 and maintainingthe cooling system at full power. Once the temperature 211 declinesbelow set-point 213, the duty cycle of IC 215 increases and the TTLoutput of AND gate 230 alternates between “high” and “low” and thesystem settles to keep temperature 211 close to set-point. Once theprocess is resumed, hydrazine utilization drives reservoir pressure 221down and the TTL output from comparator 224 increases. The combined dutycycle at gate 230 increases and the system is soon running substantiallyin heating mode. Once the temperature exceeds the temperature set-point,the TTL duty cycle of 215 goes down to zero and the system is back toessentially controlling on pressure.

It is also preferred to implement, as part of the method, anartificially large reservoir pressure set-point following a long idletime. For example, the embodiment described by way of example above mayuse a pressure set-point of 130 Torr within the first wafer run after alonger than usual idle time in order to artificially switch the HC zone113 to heating as early as possible to accommodate the possibly low(e.g., 120° C. or 140° C.) starting zone 113 temperature. This higherreservoir pressure set-point should be set higher than the ˜120 Torrthat the reservoir settles on during the idle time. As detailed above,that recipe modification enables zone 113 to switch into heating some160 seconds earlier. The first recipe may then switch back to areservoir pressure set-point of 100 Torr after several minutes to avoidover-production of hydrazine.

Notably, effective hydrazine abatement by mixing with strong oxidizerssuch as ozone should be preferably implemented to eliminate hydrazinefrom the process and vent exhaust. For example, the highly reactivehydrazine is rather easy to convert into products such as N₂, and waterby a simple mixing with an ozone/oxygen/nitrogen gas mixture at theexhaust of a vacuum pump after the exhaust is highly diluted down tovery low concentrations of hydrazine to ensure mild generation of heatand an easy to control abatement reaction. For example, pump 154 may bea standard fore-pump, such as a dry-pump. Typically, such dry pumpsimplement substantially high flows of nitrogen purge at the level of atleast 5 standard liters per minute (sLm) that are sufficient to dilutetypical levels of hydrazine emission between 1−10×10⁻⁴ grams/sec down to0.08-0.8% v/v concentrations. At that level of dilution, adding a5:45:50 mixture of O₃:O₂:N₂ at 1-2 sLm effectively converts virtually100% of the hydrazine into by-products within a less than 1 meter longstainless steel exhaust line without any noticeable temperature rise orother indications of out-of-control reactions. The flow of abatement gasinto the pump exhaust as well as the concentration of ozone arepreferably monitored to ensure the availability of proper hydrazineabatement at all time. Preferably, pump purge within proper range ismonitored by the pump as part of the pump OK interlock system. Theproduction of hydrazine is preferably interlocked for the properavailability of pump 154 and abatement gas.

Preferably, both valves 123 and 144 are normally-open, meaning that theywill automatically open by reverting to the normal position in the eventof power loss or a triggered interlock. In order to produce hydrazine,valves 123 and 144 are commanded to shut and valve 125 is commanded toopen. In order to deliver hydrazine to the process, valve 130 iscommanded open. During process, valve 171 is opened as needed perprocess specifications. Downstream from valve 130, an additionalpressure controller such as a MKS series 640A (not shown) can beimplemented to reduce the pressure even further for improvedconsistency, or otherwise to obtain a lower dew-point temperature fordelivery lines 142. Similarly, for some processes, an MFC downstreamfrom valve 125 may be implemented to support flow control delivery forprocesses such as CVD. In some cases, flow sensors can also serve tocontrol the production of hydrazine if implemented in serialcommunication between source chamber 127 and valve 130.

As taught in the illustrative embodiment above, interlocks may triggerthe release of excess hydrazine from reservoir 121 and/or source chamber127 into pump manifold 150. For example, this may occur if excesspressure within reservoir 121 exceeds the upper limit set for pressuregauge 122. This hard-wired operation may release a substantial quantityof hydrazine into the pump exhaust within several seconds. For example,vent of accumulated 0.1 grams of hydrazine within 5 seconds is possible.At that level, hydrazine concentration excursion to the 15-20% levelmomentarily may exceed the 1-2% concentration of ozone used forabatement. The low concentration of ozone mixed into the exhaust flowkeeps the reaction slow and extends the conversion time of the hydrazineexcursion by a factor of 10 in ˜1 minute. To accommodate the excursions,the exhaust should comprise a properly sized volume such as at least 7 Lin the case of total exhaust flow of ˜7 sLm, as described above. Forexample a 1.93 inch inner diameter (ID) exhaust line (2 inches outerdiameter (OD)) should be at least 160 inches long. Alternatively, it isrecommended to include a wide section within the exhaust line to ensurethe proper handling of hydrazine vent excursions such as a 10 inch long,8 inch OD section. This larger than 7 L exhaust provides sufficientresidence time for hydrazine to mix with sufficient quantities of ozoneto completely abate a hydrazine concentration surge. Downstream from thehydrazine abatement section, ozone removal by catalytic conversion asknown in the art is recommended. In addition, handling the by-productsof hydrazine abatement, particularly minute quantities of NO and NO₂,should be handled as known in the art. For example, small quantities maybe handled by properly sized activated carbon filters such as a sequenceof BE and K type activated carbon filters made by Asura Filters (Rowley,Mass., USA). Alternatively, wet scrubbers, typically available in somemanufacturing environments, such as semiconductor factories, may beused. The scrubbed exhaust should be monitored for below TLV emissionsof all possible components including hydrazine, ammonia, NO, and NO₂,and the production of hydrazine should preferably be interlocked to shutdown if above TLV levels of any of these substances is detected.

Advantageously, the leftover CA/HC from a used-up cartridge 110 can berecycled by a chemical manufacturer using a simple, low cost process.For example, the used-up cartridge 110 may be isolated with manual valve112 and shipped to the chemical supplier. At the chemical plant, thecartridge 110 may be filled with a solvent such as DMSO to dissolve theCA and precipitate the leftover HC. The solution and the precipitationmay then be collected and added to a chemical reactor wherein thesolution is heated to 100-120° C. Next, hydrazine may be slowly added tothe reactor and the HC allowed to precipitate. Hydrazine addition isterminated as soon as it no longer promotes any more HC precipitation.At that point, a small quantity of CA is added to precipitate allleftover hydrazine. Subsequently, the HC precipitation is separated,washed, dried, and outgassed extensively under vacuum and temperature(e.g., 100° C. for 10 hours wherein production of hydrazine isnegligible at 7×10⁻¹³ grams/sec/gram-HC or 2.5×10⁻⁵ grams/10-hours).This negligible production is equivalent to 0.05 Torr pressure risewithin a 0.25 L reservoir. Nevertheless, it is recommended to implementhydrazine abatement as described above.

This recycling procedure substantially reduces the cost of HC to aboutthe cost of hydrazine and the cost to recreate HC. The cost of hydrazinein large quantities is presently about $0.25-0.5/gram. Assuming a lotcharge for recycling 1000 grams HC and 7200 grams CA (which might beleft over after consuming 90% of 10 kg load of HC) of $1000, the totalcost for 1 kg HC is estimated to be ˜$145-190. One kg of HC will produce˜180 grams of hydrazine assuming 90% consumption. Accordingly, with thatcost, the 0.06 grams of hydrazine required to grow 50 nm of TiN per theexample above will cost 5-6 cents. Additional costs for the film includeup to 150 kJ or 0.04 kilowatt-hours (kWh) at an average commercialelectricity cost of ˜10 cents/KWh or <0.5 cents. Estimated cost of thesource at $30,000 amortized over 5 years or ˜34,000 runs/year (at 80%uptime) adds ˜18 cents to the film cost. Assuming miscellaneousadditional costs of maintenance, overhead, safety, etc. at $20,000/yearadds ˜12 cents to the cost. The total cost is therefore estimated at$0.36/film. This cost is very competitive. The hydrazine material costfraction in this embodiment is <17%.

Hydrazine production from HC heating will require many conditions thatare recommended to be hard-wire interlocked, as know in the art. Inparticular, any one of the following conditions should preferablyinterrupt power to the HC heaters and disallow the shutting down of thecooling, effectively, cooling down cartridge 110. These conditions are:

1. Temperature in zone 128 below set-point;

2. Temperature in zone 141 below set-point;

3. Temperature in zone 172 below set-point;

4. Pressure at 151 above set-point (meaning faulty vent manifold 150);

5. Pump 154 not working properly;

6. Abatement module 155 not working properly;

7. Hazardous gas monitor(s) 156 reading hydrazine, NO, NO₂, etc. aboveTLV;

8. Facilities gas monitors or any other facilities interlock not OK;

9. Valve 144 not shut;

10. Valve 123 not shut;

11. Over pressure at pressure gauge 122;

12. Zone 113 snap switches above set-point; and

13. Cartridge cooling apparatus not working.

These and various other conditions, and the response of the apparatus100 thereto, are compiled in Table 1:

TABLE 1 Device status: Device Zone Valve Valve Valve Valve ValveSituation 113 123 125 130 144 153 Valve 112 shut cool O C C O O Pressure122 < set-point heat C N/A N/A C O Pressure 122 ≧ set-point cool C N/AN/A C O Zone 113 over-temperature cool O C C O O Zone 128 undertemperature cool O C C O O Zone 141 under temperature cool O C C O OZone 172 under temperature cool O C C O O Pressure 129 < set-point N/AN/A O N/A N/A O Pressure 129 ≧ set-point N/A N/A C N/A N/A O Pressure151 < set-point N/A N/A N/A N/A N/A O Pressure 151 ≧ set-point cool C CC C C Pump 154 fault cool C C C C C Abatement 155 fault cool C C C C CHazardous gas 156 - goes off cool C C C C C Power loss cool O C C O CFacilities hazardous gas cool C C C C C detection where “C” indicatesthat a valve is closed, and “O” indicates that a valve is open.

Several processes in accordance with illustrative embodiments of theinvention using on-demand hydrazine are now described. The processconditions for these embodiments are summarized in Table 2.

TABLE 2 Summary of source apparatus and method parameters for severalexemplary processes Deposition Process time/ Reservoir Initial HC FinalHC No. rate Thickness HC load idle time Hydrazine volume^(b)/temperature during temperature during of runs Process (nm/min) (nm) size(Kg.) % usage (min) usage rate^(a) pressure^(c) process (° C.) process(° C.) per load TiN ALD 10 50 1 90 5/2 1.2 0.25/100 186 207 5,000 Copper3 18 1 90 4/3 2  0.5/100 191 212 2,500 ALD SiO₂ ALD 7.5 30 1 90 4/2 5 0.5/200 199 221 1,500 Platinum 6 5 1 90 1/2 2 0.25/100 191 212 18,000ALD SiN CVD 20 50 2 95 2.5/2   5   1/100 193 221 5,000 Clean and N/A N/A1 90  1/6^(d) 5 0.25/100 199 221 6,000 activation Post N/A N/A 1 90  1/6^(e) 5  0.5/200 188 209 1,500 deposition treatment Reactive N/A N/A1 90 4/3 2  0.5/100 191 212 2,500 abatement of TiCl₄ or WF₆ ^(a)× 10⁻⁴grams/sec. ^(b)Liters ^(c)Torr ^(d)The pre-process idle time comprisesthe process time + the idle time ^(e)The post-process idle timecomprises the process time + the idle timeExemplary Process No. 1—ALD of TiN:

An ALD deposition of TiN (i.e., titanium nitride) applies sequentialreactions of TiCl₄ and hydrazine. The sequence of TiCl₄ and hydrazinegrows 0.05 nm/cycle with an optimized cycle time of ˜0.5 seconds. Fiftynm of TiN is applied in this example as a top capacitor electrode or abarrier. A process time of 5 minutes at 1.2×10⁻⁴ grams/sec hydrazineinitially pins the temperature of a 1 kg HC load at 186° C., increasingto 207° C. after the exhaustion of the source down to 10% potency.During a 2 minute idle time, the source temperature drops ˜6° C. with100 W cooling and the 0.25 L reservoir exceeds the set 100 Torr pressureby ˜25 Torr. This additional 25 Torr lasts ˜80 seconds prior to thetrigger of HC heating. Then the pressure recovers to 100 Torr withinapproximately 60 seconds. In this case, 1 kg of HC at 90% usage lasts˜5,000 8-inch wafers. Hydrazine generated in this manner was found to bemuch more effective than previously used NH₃ (ammonia) as well asmonomethyl-hydrazine and dimethylhydrazine. For example, high-qualityTiN films were grown below 300° C. at a cost-effective rate of 10nm/min.

Exemplary Process No. 2—ALD of Copper:

An ALD process for copper applies sequential reactions of a copperprecursor, such as Cu(acac)₂, Cu(thd)₂, or Cu(hfac)₂, followed byhydrazine/ozone (HOZ), and then followed by hydrazine exposure. Thethree step cycle is intended for effective removal of ligands from thecopper precursor, followed by the effective reduction of a partiallyoxidized copper surface into metal. The mixture of hydrazine and ozoneforms substantially in the vicinity of the substrate and is a veryeffective oxidizer. The sequence grows 0.075 nm/cycle with an optimizedcycle time of ˜1 second. Eighteen nm of copper is applied in thisexample as a seed layer for copper ECD. A process time of 4 minutes at2×10⁻⁴ grams/sec hydrazine initially pins the temperature of a 1 kg HCload at 191° C., increasing to 212° C. after the exhaustion of thesource down to 10% potency.

During a 3 minute idle time, the source temperature drops ˜9° C. at 100W cooling and the 0.5 L reservoir exceeds the set 100 Torr pressure by˜17 Torr. This 17 Torr lasts ˜120 seconds prior to the trigger of HCheating. Then the pressure recovers to 100 Torr within approximately 90seconds. In this case, 1 kg of HC at 90% usage lasts ˜2,500 8-inchwafers.

Exemplary Process No. 3—ALD of SiO₂

An ALD process for SiO₂ (i.e., silicon dioxide or silicon oxide) appliessequential reactions of Bis(diethylamino)silane (BDEAS) and HOZ. Themixture of hydrazine and ozone forms substantially in the vicinity ofthe substrate and is a very effective oxygen precursor. The sequence ofBDEAS and HOZ grows 0.125 nm/cycle with an optimized cycle time of ˜1second.

Thirty nm of SiO₂ is applied in this example as a corrosion protectivelayer. A process time of 4 minutes at 5×10⁻⁴ grams/sec hydrazineinitially pins the temperature of a 1 kg HC load at 199° C., increasingto 221° C. after the exhaustion of the source down to 10% potency.During a 2 minute idle time, the source temperature drops ˜6° C. at 100W cooling and the 0.5 L reservoir exceeds the set 200 Torr pressure by˜50 Torr. This 50 Torr lasts ˜90 seconds prior to the trigger of HCheating. Then the pressure recovers to 200 Torr within approximately 60seconds. In this case, 1 kg of HC at 90% usage lasts ˜1,500 8-inchwafers.

Exemplary Process No. 4—ALD of Platinum:

An ALD process for platinum applies sequential reactions of a platinumprecursor, such as (methylcyclopentadienyl)trimethylplatinum(MeCpPtMe₃), followed by HOZ. The cycle intends for effective removal ofligands from MeCpPtMe₃. The mixture of hydrazine and ozone formssubstantially in the vicinity of the substrate and is a very effectiveoxidizer. The sequence grows ˜0.1 nm/cycle with an optimized cycle timeof ˜1 second. Five nm of platinum is applied in this example as acontact for FRAM capacitor electrodes. A process time of 50 seconds at2×10⁻⁴ grams/sec hydrazine initially pins the temperature of a 1 kg HCload at 191° C., increasing up to 212° C. after the exhaustion of thesource down to 10% potency. During a 2 minute idle time, the sourcetemperature drops ˜4° C. at 50 W cooling and the 0.25 L reservoirexceeds the set 100 Torr pressure by ˜30 Torr. This extra 30 Torr dropsdown 21 Torr during the deposition of the next wafer while thetemperature decreases further by an additional ˜2° C. In the next idletime the temperature drops an additional ˜4° C. to a total of 10° C. Thepressure increase during that idle time is ˜14 Torr, causing thereservoir pressure to reach 123 Torr. In the next process/idle cycles,the zone 113 temperature keeps dropping until it eventually settles at˜180° C. In this case, 1 kg of HC at 90% usage lasts ˜18,000 processruns.

Exemplary Process No. 5—CVD of SiN:

A CVD process for SiN (i.e., silicon nitride or Si₃N₄) applies thereaction of reactive silicon precursors, such as hexachlorodisilane,trisilane or disilane, with hydrazine. The process grows 50 nm within2.5 minutes (20 nm/min). A process time of 2.5 minutes at 5×10⁻⁴grams/sec hydrazine initially pins the temperature of a 2 kg HC load at193° C., elevating up to 221° C. after the exhaustion of the source downto 5% potency. During a 2 minute idle time, the source temperature drops˜6° C. at 100 W cooling and the 1 L reservoir exceeds the 100 Torrset-point pressure by ˜20 Torr. This 20 Torr lasts ˜60 seconds prior tothe trigger of HC heating. Then the pressure recovers to 100 Torr withinapproximately 60 seconds. A 2 kg load of HC at 95% usage lasts ˜5,0008-inch wafers. Hydrazine generated in this manner was found to be muchmore effective than NH₃ (ammonia), used to grow SiN previously.

Exemplary Process No. 6—Pre-Process Surface and Parts Treatment;Substrate Preparation for ALD with Functionality Groups; PCB andPlastics Cleanup and Activation:

Pre-process surface cleaning and surface activation processes apply aco-exposure of HOZ or hydrazine for the in-situ removal of contaminationand for the population of the surface with reactive terminations such ashydroxyl or amine groups. The mixture of hydrazine and ozone formssubstantially in the vicinity of the substrate and is a very effectiveoxidizer. Hydrazine is also an effective reducer and/or nitridizer. Aprocess time of 1 minute at 5×10⁻⁴ grams/sec hydrazine initially pinsthe temperature of a 1 kg HC load at 199° C., elevating up to 221° C.after the exhaustion of the source down to 10% potency. During asubsequent process time and idle time (where hydrazine is not utilized),the pre-processing source is idle. For example, a total of 6 minuteselapses between successive surface cleaning/activation operations. Toaccommodate such small duty cycle applications, a preferable methodsimply uses the hydrazine already in the reservoir without heating theHC while the pre-processing operation is in progress. After thepre-processing operation, the hydrazine is replenished by slowly heatingthe HC. For example a 0.25 L reservoir is controlled to a set-pointpressure of 100 Torr. During the 1 minute pre-processing operation, thereservoir pressure drops to 36 Torr. Subsequently, the pressure isrecovered during the 6 minutes idle time. To replenish the draw ofhydrazine during the 6 minute idle time, a 1 kg HC load is initiallyheated to 183° C., elevating up to 204° C. after the exhaustion of thesource down to 10% potency. In this case, 1 kg of HC at 90% usage lasts˜6,000 8-inch wafers.

Exemplary Process No. 7—Post Deposition Treatments:

Post-deposition treatment to improve films and materials appliesco-exposures of HOZ or hydrazine for the in-situ improvement of manyproducts. The mixture of hydrazine and ozone forms substantially in thevicinity of the substrate and is a very effective oxidizer. Hydrazine isalso an effective reducer and/or nitridizer. A process time of 20-600seconds at 0.1−5×10⁻⁴ grams/sec hydrazine initially pins the temperatureof a 1 kg HC load at a temperature in the range of 180-210° C.,elevating up to 230° C. after the exhaustion of the source down to 95%potency. During a subsequent process and idle time (where hydrazine isnot utilized), the post-treatment source is idle. For example, a totalof 7 minutes elapses between successive post-treatment operations. Toaccommodate such small duty cycle applications, a preferable methodsimply uses the hydrazine already in the reservoir without heating theHC while the post-treatment operation is in progress. After thepost-treatment operation, the hydrazine is replenished by slowly heatingthe HC. For example, a 0.5 L reservoir is controlled to a set-pointpressure of 200 Torr. During the 2 minute post-treatment operation, thereservoir pressure drops to 72 Torr. Subsequently, the pressure isrecovered during the 7 minute idle time. To replenish the draw ofhydrazine during the 7 minute idle time, a 1 kg HC load is heated to188° C., elevating up to 209° C. after the exhaustion of the source downto 10% potency. In this case, 1 kg of HC at 90% usage lasts ˜1,500sequences.

Exemplary Process No. 8—Reactive Abatement of TiCl₄ and WF₆:

During the ALD or CVD of TiN and TiO₂, and the ALD and CVD of W and WN,unused TiCl₄ and WF₆ can be abated downstream from the process chamber,as described in US Patent Publication No. 2007/0012402, entitled“Apparatus and method for downstream pressure control andsub-atmospheric reactive gas abatement,” to one of the currentinventors. This integrated reactive abatement process applies thereaction of reactive hydrazine and HOZ to effectively convert thereactive chemicals into solid inert deposits such as TiN, TiO, W, and WNover a high area abatement trap. The abatement process is carried outduring the deposition process. For example, the deposition process maytake 4 minutes and the idle process may take 3 minutes. In such a case,a 1 kg HC load at ˜191° C. produces 2×10⁻⁴ grams/sec hydrazine forabatement when the source is fresh, elevating up to 212° C. after theexhaustion of the source down to 10% potency. During the 3 minute idletime, the source temperature drops ˜9° C. at 100 W cooling and the 0.5 Lreservoir exceeds the set 100 Torr pressure by ˜17 Torr. This 17 Torrlasts ˜120 seconds prior to the trigger of HC heating. Then the pressurerecovers to 100 Torr within approximately 90 seconds. In this case 1 kgof HC at 90% usage lasts ˜2,500 8-inch wafers.

It should again be emphasized that the above-described embodiments ofthe invention are intended to be illustrative only. Other embodimentscan use different chemical species, different types and arrangements ofelements, and different method steps for implementing the describedfunctionality. For example, while the above-described embodiments aredirected at producing hydrazine, other hazardous reactants including,but not limited to, arsine, phosphine, tungsten hexafluoride, borontrichloride, silane, disilane, trisilane and diborane may be safelyproduced using apparatus and methods in accordance with aspects of theinvention. One skilled in the art will recognize the various chemicalcomplexes that may be used to evolve these various reactants. Moreover,the chemical transformation of such reactants into stable chemicalcomplexes is further described by G. B. Seifer in “Cyanuric Acid andCyanurates,” Russian Journal of Coordination Chemistry, 28, 2002, p.301, which is hereby incorporated by reference herein. These numerousalternative embodiments within the scope of the invention will beapparent to one skilled in the art.

In so much as aspects of the present invention teach methods ofmanufacture, the invention is further intended to encompass products ofmanufacture that are formed at least in part using these methods.Moreover, all the features disclosed herein may be replaced byalternative features serving the same, equivalent, or similar purpose,unless expressly stated otherwise. Thus, unless expressly statedotherwise, each feature disclosed is one example only of a genericseries of equivalent or similar features.

What is claimed is:
 1. An apparatus for providing a reactant, theapparatus comprising: a reactant space comprising a chemical complexcapable of evolving the reactant in the reactant space via thermaldecomposition when heated; a reservoir space in gas communication withthe reactant space; a vacuum pump in gas communication with thereservoir space through one or more valves; and control circuitryconfigured to heat the chemical complex when a pressure of the reactantin the reservoir space is below a predetermined set-point, and to coolthe chemical complex when the pressure of the reactant in the reservoirspace is above the predetermined set-point; and to place the reservoirspace in open connection with the vacuum pump and to cool the chemicalcomplex if a fault related to falling below a preset temperature in aheated portion of the apparatus is detected.
 2. The apparatus of claim1, wherein the apparatus further comprises a source space, the sourcespace being in gas communication with the reservoir space through apressure control valve.
 3. The apparatus of claim 2, wherein thepressure control valve is operative to maintain the source space at apressure lower than the pressure of the reservoir space.
 4. Theapparatus of claim 1, wherein the apparatus further comprises a sourcespace, the source space being in gas communication with the reservoirspace through a mass flow controller.
 5. The apparatus of claim 1,wherein the apparatus is further operative to maintain the chemicalcomplex above a predetermined temperature.
 6. The apparatus of claim 1,wherein the apparatus is operative to heat the chemical complex by atleast one of heated fluid, resistive heating, and radiant heating. 7.The apparatus of claim 1, wherein the apparatus is operative to cool thechemical complex by at least one of circulated gas and cooled fluid. 8.The apparatus of claim 1, wherein the apparatus is operative to limitthe temperature of the chemical complex to a maximum predeterminedtemperature.
 9. The apparatus of claim 1, wherein the temperature of thechemical complex is monitored by one or more temperature snap switches.10. The apparatus of claim 1, wherein each of one or more portions ofthe apparatus is heated to a temperature above a respective dew point ofthe reactant at that respective portion.
 11. The apparatus of claim 10,wherein the temperature of each heated portion is monitored by one ormore respective temperature snap switches.
 12. The apparatus of claim 1,wherein the apparatus is adapted to isolate the reservoir space from thevacuum pump if a fault is detected with the vacuum pump.
 13. Theapparatus of claim 1, wherein the vacuum pump causes any of the reactantpumped by the vacuum pump to be diluted with another chemical species.14. The apparatus of claim 13, wherein the another chemical speciescomprises nitrogen.
 15. The apparatus of claim 1, further comprising anabatement portion downstream of the vacuum pump, the abatement portionoperative to cause substantially all of any of the reactant that ispumped by the vacuum pump to be chemically converted.
 16. The apparatusof claim 15, wherein the abatement portion is operative to react any ofthe reactant that is pumped by the vacuum pump with at least one ofozone and oxygen.
 17. The apparatus of claim 1, wherein the reactant hasNational Fire Protection Association (NFPA) flammability and instabilityratings greater than or equal to three, and the chemical complex hasNFPA flammability and instability ratings less than or equal to one. 18.The apparatus of claim 1, wherein the reactant comprises hydrazine. 19.The apparatus of claim 1, wherein the chemical complex compriseshydrazine cyanurate.
 20. The apparatus of claim 1, wherein the reactantis arsine, phosphine, tungsten hexafluoride, boron trichloride, silane,disilane, trisilane, ClF₃ or diborane.
 21. The apparatus of claim 1,wherein the reactant space comprises a removable cartridge that housesthe chemical complex while keeping the chemical complex chemicallyisolated from any ambient gases that surround the removable cartridge.